Alpha-1-antitrypsin deficiency in children: liver disease is not reflected by low serum levels of alpha-1-antitrypsin - a study on 48 pediatric patients

BACKGROUND

Alpha-1-antitrypsin (alpha1-AT) is an important protease inhibitor. The phenotypes are characterized by a low total serum alpha1-AT or by an abnormal protein accumulating in the hepatocytes. The aim of our study was to examine a correlation of total serum alpha1-AT, phenotype, and liver involvement in pediatric patients.

METHODS

48 patients, deficient for alpha1-AT were included. The phenotypes for alpha1-AT were determined by isoelectric focusing. Liver disease was defined either as elevated transaminases or/and as elevated conjugated bilirubin and gammaGT. Patients were reexamined after a mean interval of 2 years.

RESULTS

Homozygous alpha1-AD was found in 12 patients, heterozygous in 24 patients. In 12 children rare variants of alpha1-AD were diagnosed. Serum alpha1-AT levels less than 60% of normal were found in all patients with homozygous, in 37% of patients with heterozygous alpha1-antitrypsin deficiency (alpha1-AD), and in patients with the homozygous variant PiM(palermo). Liver disease was found in 8/12 patients with the phenotype PiZZ and in 15/24 patients with heterozygous alpha1-AD. Three of 4 patients with the phenotype PiMQ0 had severe liver disease despite normal serum levels for alpha1-AT. In 11 patients with heterozygous alpha1-AD liver disease was apparent despite normal serum alpha1-AT levels. In two patients with the variant type Mpalermo serum levels were as low as 11% of normal without any signs of liver disease.

CONCLUSIONS

Our data clearly show that in the diagnostic workup of neonatal cholestasis measurement of total serum alpha1-AT does not exclude liver disease due to abnormal alpha1-AT variants. We suggest analysis of alpha1-AT-phenotype by isoelectric focussing in patients with unknown liver disease. Heterozygous or rare variant types might remain undiagnosed by measuring total alpha1-AT only.

Renal function and renotropic effects of secretin in cystic fibrosis

In ten cystic fibrosis patients and nine age-matched controls, renal function was determined before and after infusion of secretin. Under baseline conditions creatinine excretion and clearance were significantly elevated, exclusively due to those patients who were homozygous for the DF508 mutation (153 vs 132 ml/min*1.73m2), whereas the glomerular filtration rate, measured by inulin clearance showed no difference. Renal plasma flow and the fractional reabsorption rates of electrolytes were similar in patients and controls. During secretin infusion renal plasma flow increased and the fractional reabsorption rates of electrolytes decreased in both groups. The patients had a increased metabolic clearance (2900 vs 1660 ml/min*m2) and endogenous production rate (9,9 vs 2,5 pmol/min*m2) of of secretin. In conclusion global renal function and electrolyte handling, in particular chloride permeability, are unchanged in cystic fibrosis. Individuals expressing the DF508 genotype showed a selective elevation of creatinine excretion and clearance. The secretion and metabolic clearance of secretin are increased in cystic fibrosis.

MRI of primary meningeal sarcomas in two children: differential diagnostic considerations

Meningeal sarcomas are very rare, highly aggressive tumours affecting children more frequently than adults. The clinical course and MRI of meningeal sarcomas in two cases are discussed with special regard to possible misinterpretation. In one case MRI demonstrated a circumscribed mass in contact with the meninges, with central areas of haemorrhage. In the other, a case of primary leptomeningeal sarcomatosis, several MRI examinations over the course of almost a year were unhelpful, despite severe neurological complaints. Then MRI revealed meningeal contrast enhancement all over the brain and spinal canal, together with cerebral infarcts. MRI of meningeal sarcomas has not been discussed in the literature. MRI did not permit specific diagnosis, but enabled visualisation of the extent of the tumour and/or meningeal involvement. Early histological diagnosis is indispensable for adequate treatment.

A recombinant polypeptide model of the second predicted nucleotide binding fold of the cystic fibrosis transmembrane conductance regulator is a GTP-binding protein

Association reactions of a recombinant CFTR-NBF-2 polypeptide fused to glutathione S-transferase with guanine nucleotides were monitored quantitatively by recording the fluorescence enhancement of excited trinitrophenol (TNP)-labelled GTP after binding to NBF-2. Binding of TNP-GTP to the recombinant NBF-2 polypeptide was characterized by a Kd value of 3.9 microM. The corrected Kd values for unlabelled guanine nucleotides were determined to be 33 microM for GTP, 92 microM for GDP and 217 microM for GMP. TNP-ATP bound to NBF-2 was competitively displaced by GTP indicating a common binding site for both nucleotides. The recombinant NBF-2 did not show an intrinsic GTPase activity above a detection limit of 0.007 min(-1). Our findings provide the first experimental evidence that NBF-2 can act as a GTP-binding subunit that would favor the release of GDP after GTP hydrolysis.

Expression and functional properties of the second predicted nucleotide binding fold of the cystic fibrosis transmembrane conductance regulator fused to glutathione-S-transferase

CFTR-NBF-2 was expressed in Escherichia coli in fusion with glutathione-S-transferase, the soluble portion was purified and identified as a structured protein by its CD spectrum. Association reactions of the recombinant NBF-2 with adenine nucleotides were monitored qualitatively by demonstrating its ability to bind specifically to ATP-, ADP- and AMP-affinity agarose and quantitatively by recording the fluorescence enhancement of excited trinitrophenol (TNP)-labelled adenine nucleotides occurring as a result of binding to NBF-2. Best-fit monophasic binding curves to the fluorescence data indicated Kd values of 22 microM for TNP-ATP, 39 microM for TNP- ADP and 2.1 microM for TNP-AMP. The corrected Kd values for unlabelled adenine nucleotides competing with the fluorophores were determined to be 37 microM for ATP, 92 microM for ADP and 12 microM for AMP. The recombinant NBF-2 did not show any hydrolytic activity on ATP (detection limit 0.001 s-1). Our findings support the concept of a central role of NBF-2 in CFTR activity regulation acting as an allosteric switch between channel opening and closing and give the first experimental evidence that the channel inhibitor AMP could act via NBF-2.

Mutation analysis in the diagnosis of cystic fibrosis

Since the characterization of the gene encoding the cystic fibrosis transmembrane conductance regulator protein and identification of its main mutation, delta F508, causing cystic fibrosis (CF), more than 150 mutations in this gene have been reported, most of them only in a few or even single CF patients. Attempts to use mutation analysis in genetic counselling or for the diagnosis of CF depends on prevalence data of certain mutations in the respective population, and considerable ethnic differences have been reported. In this study we determined the prevalence of the mutations delta F508, G551D, R553X, and G542X and of genotypes defined by these mutations in 239 CF patients (444 independent CF chromosomes) seen in our clinic. The analysis for those four mutations alone now permits identification of approximately 75% of all mutations in our CF patients. The complete genotype can be resolved in approximately 63% of patients. This represents the diagnostic sensitivity which can be achieved by mutation analysis in patients without a family history of CF. We conclude that in situations where conventional diagnostic tests are not feasible or difficult to interpret, mutation analysis using a limited set of mutations can contribute significantly to an early and specific diagnosis of CF.

Multiple respiratory chain abnormalities associated with hypertrophic cardiomyopathy and 3-methylglutaconic aciduria

In a 4.5-month-old boy presenting with marked muscular hypotonia in the neonatal period, hepatomegaly, cardiac hypertrophy, recurrent hypoglycemia, metabolic acidosis, and secondary carnitine deficiency, there was a considerable urinary excretion of 3-methylglutaconic and 3-methylglutaric acid. Estimation of 3-methylglutaconyl-CoA hydratase, 3-hydroxy-3-methylglutaryl-CoA lyase and initial enzymatic steps of cholesterol biosynthesis in cultured fibroblasts and in different tissues postmortem revealed no enzyme deficiency. Analyses of the respiratory chain in postmortem tissues demonstrated severe impairment of complex I (NADH ubiquinone oxidoreductase) and complex IV (cytochrome c oxidase) activities in skeletal muscle and reduced complex IV activity in heart.

Hartnup syndrome, progressive encephalopathy and allo-albuminaemia. A clinico-pathological case study

Clinical, biochemical, neuropathological and neurochemical findings in a case of Hartnup syndrome are reported. After initially normal development, the affected girl suffered progressive neuropsychiatric decline with statomotor and mental retardation and intractable seizures and died at the age of 2 years. Postmortem neuropathological and neurochemical investigations showed a combination of extensive neuronal degeneration and cerebral dysmyelination. Pathogenetic hypotheses and the relationship between neuropsychiatric disease and Hartnup syndrome are discussed. Additionally, a fast type bisalbuminaemia present in the girl and her mother is described.

Vitamin D dependent rickets type II with myelofibrosis and immune dysfunction

We present a new patient with vitamin D dependent rickets type II. A 20-month-old Arabian boy whose parents are first cousins showed florid rickets, myelofibrosis and recurrent septicaemia. In addition to absent specific binding for 1,25-dihydroxyvitamin D3 (1,25(OH)2D3). 25-Hydroxyvitamin D3-24-hydroxylase activity could not be induced in cultured fibroblasts. The patient did not respond to 99 micrograms 1,25(OH)2D3 per day, but skeletal and haematological abnormalities improved with daily infusion of 100 mg/kg calcium, as serum parathyroid hormone levels fell to normal values. At the age of 7 years, he died from pneumonia. The improvement of haematological abnormalities with calcium infusions but not with 1.25(OH)2D3 suggests a pathogenetic relationship of myelofibrosis and hyperparathyroidism. Having anti-lipid A IgM antibody titres up to 1:10.000 after Gram negative septicaemias, the patient never produced corresponding IgG antibodies. His neutrophil chemotaxis was persistently reduced to 57% +/- 3% of age-matched controls (P less than 0.028). The patient showed two pathological immune functions considered to contribute to the well-known susceptibility to infection in rickets.

[Physiopathology of the exocrine pancreas in children]

The mechanism leading to exocrine pancreatic disease in children differs from those encountered in adult patients: I. In acute pancreatitis autodigestion of the gland by proteolytic enzymes may occur and two mechanisms may play a role. 1. Reflux of biliary secretions (e.g. in malformations of the duct system) facilitates activation of trypsinogen by enteropeptidase and leads to the presence of active proteolytic enzymes in the gland (exogenous activation). 2. Lysosomal enzymes may play a role in the intracellular activation of zymogens if inflammation leads to a fusion of lysosomes with zymogen granules (endogenous activation). II. In chronic relapsing and hereditary pancreatitis malformations of the pancreatico-biliary duct system must be sought because surgery may be indicated (common channel syndrome and choledochal cysts). III. Among the hereditary diseases leading to pancreatic insufficiency cystic fibrosis (CF) plays the main role. Haplotype analysis has shown that two genetically different types of CF exists (PS and PI). The pancreas shows manifest insufficiency only in the PI-types which occur in more than 70% of cases but the distribution of haplotypes is different in different ethnic groups. In spite of the recent discovery of the cystic fibrosis gene the exact mechanism leading to exocrine pancreatic dysfunction in CF is not clear, but diminished chloride and bicarbonate secretion, may be the result of a disturbance in the regulation of chloride channels, on acinar or ductular level. In the Shwachman-Diamond syndrome a very severe type of exocrine insufficiency with unknown etiology is encountered at birth.

Replacement therapy for a homozygous protein C deficiency-state using a concentrate of human protein C and S

A severe congenital deficiency of protein C was diagnosed in a 10-month-old girl who had been suffering from skin necrosis since the age of 7 months. The patient was treated initially with fresh frozen plasma, 10 ml per kg body weight, every 24 h. Following treatment, the mean plasma level of protein C was 0.1 U/ml after 30 min and less than 0.02 U/ml after 24 h. The child was then treated with a concentrate of human protein C and S, 100 U protein C per kg body weight, given every 48 h for a period of 9 months. The mean plasma level of protein C was 0.93 U/ml 30 min after administration of the concentrate and 0.13 and 0.08 U/ml after 24 and 48 h, respectively. The mean post-transfusional in vivo recovery of protein C was 44% and the half life was 8.3 h. The mean plasma level of 'free' protein S increased from 1.1 to 2.2 U/ml after administration of the concentrate. There was no increase in 'bound' protein S. The in vivo recovery of 'free' protein S was 49% and the half life was about 17 h. Since the start of this replacement therapy using a human protein C and S concentrate, the patient has not developed any thromboembolic complications. These results indicate the therapeutic value of human protein C and S concentrate in the treatment of severe protein C deficiency.

Hormone-elicited enzyme release by the small intestinal wall

Three enzymes of intestinal origin-enterokinase, alkaline phosphatase, and sucrase-were released into the perfused small intestinal lumen of the rat upon intravenous injection of the gastrointestinal hormone cholecystokinin-pancreozymin (CCK-PZ). The presence of bile in the perfusion fluid greatly augmented this release. The results suggest that a combined mechanism of enzyme liberation due to direct hormonal stimulation of the gut wall and further solubilization of released intestinal enzymes by bile may be responsible for the appearance of these enzymes in the gut lumen.